Water Pollution and Its Effects on Aquatic Animal Life

Abstract

Polluted water places sustained pressure on animals living in rivers, lakes, estuaries and seas. Their survival depends on fairly steady water conditions, especially enough dissolved oxygen, moderate nutrient levels, suitable pH, clear water and limited exposure to toxins. This paper discusses the effects of sewage, farm runoff, industrial discharge, metals, pesticides, oil, plastics and microplastics, pharmaceuticals and endocrine-active compounds on fish, crustaceans, molluscs, plankton, bottom-dwelling organisms, marine mammals and other aquatic fauna. The review shows that organic wastes raise biochemical oxygen demand and draw down dissolved oxygen, whereas excess nutrients promote eutrophication, algal blooms, hypoxia and fish mortality. Chemical contaminants can injure gills, liver, kidneys, nervous tissue, DNA and reproductive organs. Long-lived pollutants, especially methylmercury, build up in organisms and become more concentrated along food chains. Microplastics can be swallowed and may carry harmful chemicals, while oil pollution can smother animals, harm early life stages and contaminate habitats. Evidence from the Gulf hypoxic zone, Minamata mercury contamination, the Deepwater Horizon spill and polluted river stretches in India shows that pollution can cause sudden deaths as well as gradual biodiversity loss. The paper concludes that protection of aquatic animals depends on better wastewater treatment, nutrient control, industrial regulation, plastic-waste reduction, enforcement of environmental laws and restoration of damaged habitats.